454 



THE AMERICAN NATURALIST [Vol. LI 



III. Separability in velocity, hiocharacter motion (/. e., 



rate of transformation, or relative displace- 

 ment). 



1. Ontogenetic acreleratio)!, hastening? of develop- 



ment in ontouony, rosultinp^ in certain biocliar- 

 acters a])i)eai'iMi>' at earlier and earlier stages 

 of develoi)nuMit. Uyntt's law. 



2. Ontogenei i< id nrthtl nm , slowing down of bio- 



characters 111 iiiit(»ucii\ , resulting in certain 

 biocliaraclcrs appearing at later and later 

 stages of develoi)ment. Hyatt's law. 

 1 andg2 result in heterochrony (Gegenbaur). 



3. Ontogenetic balance, resulting in biocharacters 



a])])earing at the same stage as in the ances- 

 tral forms. 



4. I'}i//h)//< IK fi< (1(1 ele nit ion, a])i)earaiice of certain 



liom()moi'])]iic biocharactei-s at earlier geologic 



5. Phylogcuit,, ,>l,n>hitnni. ul.ccl.v -.ome homo- 



morpliic hiodia rad rr> appear at later geologic 

 periods ill M.HM' plivla than ..Hum-. 



IV. SeiUUahlhhl >U (n>u,/>nn/, I'U.lnlnuh, ,nn,ni.,t>nn 



